Isotopes/Transcript
Transcript Text reads: The Mysteries of Life with Tim and Moby Tim and Moby are in a classroom. There is a periodic table of elements on the wall. Tim has his back to the table, and he is blindfolded. He is trying to recite the names of the elements as Moby follows along. TIM: Hydrogen, helium, lithium, um... beryllium, boron, ah... nitrogen? MOBY: Beep. TIM: Oh, carbon! Tim removes his blindfold. TIM: I always mess that one up. Tim reads from a typed letter. TIM: Dear Tim and Moby, how can two atoms of the same element have different numbers of neutrons? From, Gabriela. Whoa, good thing we've got the periodic table of elements handy. Let's look at an element as it's shown on the table. How about, oh, say, chlorine. The periodic table entry for the element chlorine appears and knocks Moby over. Tim stands next to the entry. Text of the entry reads: Chlorine, seventeen, Cl, 35.453. TIM: Cl is the symbol for chlorine. Tim taps on the symbol with a pointer. TIM: And this is its atomic number, the number of protons in its nucleus. Tim uses his pointer to indicate the number 17. MOBY: Beep. TIM: The atomic number is what makes each element unique. Every chlorine atom in the universe has exactly seventeen protons. An animation shows a chlorine atom with seventeen protons in the nucleus labeled with a plus sign. TIM: One more or one less, and it becomes a different element, with totally different properties. The chlorine atom acquires one more proton and becomes an argon atom. Then the number of protons changes to sixteen, one less than chlorine. Text beneath the atom now reads: sulfur. TIM: The number of neutrons, on the other hand, can vary. An animation shows the chlorine atom with a different number of neutrons in the nucleus. MOBY: Beep. Moby's head flies off, and smoke drifts from the resulting hole. TIM: Oh, come on. It's not that big a deal. Tim replaces Moby's head on his body. TIM: Unlike protons and electrons, neutrons have no charge. We know that opposite charges attract, and like charges repel. Images represent three types of particles. The first is a proton, colored red and labeled with a plus sign, indicating a positive charge. The second is an electron, colored blue and labeled with a minus sign, indicating a negative charge. The third particle is a neutron, colored yellow with no text on it. TIM: So, ever wonder why all those protons in the nucleus clump together instead of flying apart? An animation shows a group of protons clumping together. MOBY: Beep. TIM: The answer is neutrons. Protons stick to them, just enough to overcome all that positive charge. So you can think of neutrons as a kind of glue for the nucleus! Neutrons appear within the clump of protons. TIM: But there's always more than one way to glue a bunch of protons together. Depending on how they randomly stack up, they might need more or fewer neutrons to keep from flying apart. The animation shows the nucleus with more neutrons, and then fewer neutrons. TIM: That's why all elements naturally occur in isotopes: atoms with different numbers of neutrons. Chlorine has two natural isotopes, chlorine-35, with 18 neutrons, and chlorine-37, with 20. An animation uses images and graphics to compare the two isotopes Tim describes. Both isotopes contain 17 protons, but chlorine-35 has 18 neutrons, while chlorine-37 has 20 neutrons. TIM: We identify them by their mass numbers: the sum of their protons and neutrons. Text beneath the first isotope reads: 17 plus 18 equals 35. Text beneath the second isotope reads: 17 plus 20 equals 37. TIM: Conveniently enough, those numbers also tell us each isotope's mass: 35 and 37 atomic mass units, or u. Text beneath the first isotope changes to read: 35 u. Text beneath the second isotope changes to read: 37 u. MOBY: Beep. TIM: The two isotopes are basically identical. The only difference is that Cl-37 is heaver from its two extra neutrons. An animation shows the two isotopes on a balance scale. The scale tips toward chlorine thirty-seven, showing that it weighs more than chlorine thirty-five. TIM: Which brings us to chlorine's atomic mass. It tells us how heavy the average chlorine atom is. If chlorine's isotopes were evenly divided, this number would be thirty-six. Tim uses his pointer to indicate chlorine's atomic mass on the Periodic Table. Text reads: 35.453. TIM: But Cl-35 is way more common, so the average mass is closer to 35 u. A circle graph indicates that there is more chlorine-35 in existence than chlorine-37. Text in the center of the circle graph reads: 35.453. MOBY: Beep. TIM: Nope, they're both stable isotopes, which means their nuclei never change. A Cl-35 atom will always have 18 neutrons, and a Cl-37 atom will always have twenty. An animation shows a chlorine-35 atom remaining the same while time progresses on a clock. TIM: But some combinations of neutrons and protons are unstable. These isotopes are radioactive, which means their nuclei fall apart. Besides giving off a lot of energy, radioactive decay can change the number of neutrons in the nucleus. It can also change the number of protons, turning into a completely different substance. An animation shows a nucleus falling apart as Tim describes. A chart beside the nucleus tracks the changing number of both protons and neutrons. MOBY: Beep. TIM: It's true! Some forms of radiation are extremely dangerous. But unstable isotopes have important uses, too! Carbon-14 helps us figure out the ages of fossils and ancient artifacts. Nuclear power plants use uranium-235 as fuel. And doctors use radiation to detect and treat diseases! So there you go: isotopes in a nutshell! Images show a dinosaur skull, a nuclear power plant, and a doctor x-raying a patient. MOBY: Beep. Moby taps the Periodic Table with a pointer. TIM: Don't I get a break yet? MOBY: Beep. Tim is blindfolded again, reciting elements from the Periodic Table as Moby follows along. TIM: Hydrogen, helium, lithium, beryllium, um, boron, ah. MOBY: Beep. TIM: Carbon, carbon! Category:BrainPOP Transcripts Category:BrainPOP Science Transcripts